Journal of the American Chemical Society
COMMUNICATION
Scheme 2. Synthetic Studies on Heitziamide A
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using a variety of convenient visible light sources, including ambient
sunlight. Thus, we have developed an extremely convenient strategy
for promoting electronically mismatched DielsÀAlder cycload-
ditions between electron-rich coupling partners that would other-
wise be difficult to accomplish. Further demonstrations of the
applicability of this reaction in synthesis are under development
in our laboratory.
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’ ASSOCIATED CONTENT
b
(10) The half-wave potential of 1 is +1.1 V vs. SCE. If Ru*(bpy)32+ is
not oxidatively quenched to the more strongly oxidizing Ru(III) state
(+1.3 V), the excited state itself is insufficiently oxidizing (+0.8 V) to
produce the alkene radical cation. These values are from ref 3b and:
Kalyanasundaram, K. Coord. Chem. Rev. 1982, 46, 159.
S
Supporting Information. Experimental procedures and
characterization data for all new compounds. This material is
’ AUTHOR INFORMATION
(11) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.;
von Zelewsky, A. Coord. Chem. Rev. 1988, 84, 85.
(12) Crutchley, R. J.; Lever, A. B. P. J. Am. Chem. Soc. 1980, 102, 7128.
(13) (a) Crellin, R. A.; Lambert, M. C.; Ledwith, A. J. Chem. Soc. D
1970, 682. (b) Ledwith, A. Acc. Chem. Res. 1972, 5, 133.
Corresponding Author
(14) The regiochemistry of the cycloadducts in Chart 1 is consistent
with polarization of the dienophile as shown for structure 1•+ (Scheme 1).
The umpolung polarization of alkene radical cations has been exploited in
synthetic applications by Moeller. For an excellent, concise account, see:
Moeller, K. D. Synlett 2009, 1208.
(15) Mbaze, L. M.; Lado, J. A.; Wansi, J. D.; Shiao, T. C.; Chiozem,
D. D.; Mesaik, M. A.; Choudhary, M. I.; Lacaille-Dubois, M.-A.; Wandji,
J.; Roy, R.; Sewald, N. Phytochemistry 2009, 70, 1442.
’ ACKNOWLEDGMENT
This paper is dedicated to Prof. Howard Zimmerman in
celebration of his career and his many contributions to photo-
chemistry. This research was conducted using funds from the
ACS PRF (49817-ND1), NIH (GM095666), Sloan Foundation,
Beckman Foundation, and Research Corporation. The NMR
facilities at UW-Madison are funded by the NSF (CHE-9208463,
CHE-9629688) and NIH (RR08389-01, RR13866-01).
(16) Aminium cation initiators (ref 4c) failed to produce any trace of
the cycloadduct in the same reaction time. Similarly, we also replaced
Ru(bpz)3(PF6)2 with the photosensitizer triphenylpyrilium BF4 (ref 4e)
and failed to observed significant formation of 36. See the Supporting
3
’ REFERENCES
Information for experimental details.
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dx.doi.org/10.1021/ja2093579 |J. Am. Chem. Soc. 2011, 133, 19350–19353